Medical ablation system and method of use

ABSTRACT

Cartilage and other tissues are treated by generating a plasma in an interior space of a probe and exposing the tissue to the plasma. The plasma is released through a gap in a working end of the probe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims is a continuation of U.S. patent applicationSer. No. 13/287,315 (Attorney Docket No. 33291-722.201), filed Nov. 2,2011, which claims the benefit of U.S. Provisional Application Nos.61/454,901 (Attorney Docket No. 33291-709.101), filed on Mar. 21, 2011;61/491,541 (Attorney Docket No. 33291-718.101), filed on May 31, 2011;and 61/537,483 (Attorney Docket No. 33291-722.101), filed on Sep. 21,2011, the full disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to medical instruments and systems for applyingenergy to tissue, and more particularly relates to a system for ablatingand treating damaged cartilage tissue.

BACKGROUND OF THE INVENTION

Various types of medical instruments utilizing radiofrequency (RF)energy, laser energy and the like have been developed for deliveringthermal energy to tissue, for example to ablate tissue. While such priorart forms of energy delivery work well for some applications, prior artRF and laser devices are not capable of ablating surfaces of cartilageto provide smooth surfaces. Further, such prior art devices causeunacceptable thermal damage to cartilage tissue.

What is needed are systems and methods that can controllably applyenergy to fibrillated or damaged cartilage to smooth the cartilagewithout any thermal damage to the cartilage surface layers.

SUMMARY OF THE INVENTION

A probe for ablating tissue comprises an electrosurgical working endcomprising first and second dielectric bodies and defining an interiorchamber, wherein an interface between the first and second bodies issufficiently fluid-tight to prevent liquid flow therethrough but permitplasma propagation therethrough, first and second opposing polarityelectrodes configured for creating a current path within the interface.A probe for cutting and extracting tissue, comprises an elongatedintroducer with a first channel for tissue-extraction having atermination in a working end surface, a second channel for plasmageneration having a termination in the working surface, first and secondpolarity electrodes configured for igniting a plasma in a region of thesecond channel, and a negative pressure source in communication with thefirst and second channels. A method of ablating tissue, comprisesproviding an electrosurgical working end with an interior chambercommunicating with a working surface through a space that issufficiently fluid-tight to prevent liquid flow therethrough but permitplasma propagation therethrough, igniting a plasma in or adjacent to thegap utilizing first and second opposing polarity electrodes positionedon either side of the gap, and controlling propagation of the plasmathrough the gap to interface with tissue.

Methods for treating a target tissue utilize a probe having an interiorspace and a working end with a working surface. A plasma is ignitedwithin the interior space and propagates outwardly from the workingsurface. The target tissue is exposed to the plasma for treatment,typically ablation, cutting, coagulation, resurfacing, tissue smoothingor the like.

In a first aspect of the present invention, the plasma is released fromthe interior space through a gap in the working end of the probe.Typically, a flow of saline or other conductive media is providedadjacent to or through the gap and ignited either before entering thegap or as it passes through the gap to generate the plasma. The gaptypically has an interior periphery and an exterior periphery with aspacing therebetween which is sufficiently fluid tight (resistive tofluid flow) to inhibit fluid flow but permit plasma propagation therethrough. The plasma is typically ignited by applying electrical energyto the conductive medium from opposite polarity electrodes positioned oneither side of the gap within one electrode within the interior space.For example, a first polarity electrode may be disposed in proximity tothe inner-periphery of the gap or may be disposed in a fluid channel incommunication with said inner-periphery. The second polarity electrodemay be in or on the working end in potential fluid communication withthe exterior periphery of the gap. The gap typically has a meandimension (spacing) between said interior and exterior peripheries inthe range from 0.005 inches to 0.25 inches. The total area of the gapsurfaces may be in the range from 0.01 mm² to 10 mm². The gap may haveany one of a variety of configurations, including annular, linear, oval,elongated, star shaped, and the like.

Methods of the present invention may further comprise controlling a rateof propagation of the plasma through the gap. The plasma propagationrate may be controlled by controlling a dimension of the gap, typicallya width of the gap. Alternatively or additionally, the propagation ratemay be controlled by controlling a dimension of the gap between a plasmainitiation region within the interior space and the working surface.Still further alternatively or additionally, the propagation rate may becontrolled by varying a pressure of the conductive media in the interiorspace, either by controlling the inlet pressure and/or an outletpressure of the conductive media as it flows though the interior space.

In still other embodiments, igniting the plasma may compriseestablishing a continuous “loop” flow of the conductive media throughoutthe interior space. In such embodiments, a portion of the conductivemedia is then ignited within the interior space and a remainder of theconductive medium exits the interior space. Typically, the conductivemedia enters the interior space through an inlet flow channel in theprobe while the remainder of the conductive media exits through anoutlet flow channel in the probe. The plasma which is generated withinthe interior space then exits or emerges through one or more gaps in theworking end of the probe. In such embodiments, a propagation rate may becontrolled by varying the inlet pressure, the outlet negative pressure,or a combination of both. The flows may also be controlled by varying adimension of the gap. Plasmas are typically generated by passing currentthorough opposite polarity electrodes in or near the interior space, andthe interior space may comprise a channel transition zone between theinlet and outlet channels. Typically, the channel transition zonecomprises a flow restriction, and the plasma is ignited at the flowrestriction.

In all embodiments, the plasma typically propagates from the workingsurface by a distance of less than 2 mm, usually less than 1 mm, andoften less than 0.5 mm. The temperature of the plasma will usually beless than 80° C., often less than 70° C., and frequently less than 60°C. Typically, the target tissue may be submerged in a conductive mediumwhen it is being treated by the methods disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of the ablation device corresponding to theinvention that includes an elongated shaft extending along an axis withan articulating working end.

FIG. 2 is a sectional view of a handle portion of the device of FIG. 1.

FIG. 3 is a perspective view of the distal ablation body portion of thedevice of FIG. 1.

FIG. 4 is a plan view of the distal ablation body portion of the deviceof FIG. 1.

FIG. 5A is a sectional longitudinal view of the working end of thedevice of FIG. 1 showing the slotted sleeves configured forarticulation.

FIG. 5B is a cut-away view of the working end similar to FIG. 5A showingan electrode arrangement.

FIG. 6 is a cut-away view of the distal ablation body portion of thedevice of FIG. 1 further showing fluid flow pathways.

FIG. 7 is a schematic illustration of the device of FIG. 1 introducedinto a knee joint to treat abnormal cartilage.

FIG. 8A is a longitudinal sectional view of the ablation body portion ofthe device of FIG. 1 showing fluid flows, plasma formation and the useof a low pressure chamber to provide a selected dimension of plasmapropagating from a working surface.

FIG. 8B is another longitudinal sectional view of the ablation bodyportion as in FIG. 8A with the fluid flow parameters altered to providean alternative dimension of plasma propagating from the working surface.

FIG. 9A is an illustration of a method of the invention in ablatingfibrillation in cartilage tissue.

FIG. 9B is another illustration of the method of FIG. 8A which resultsin a smooth cartilage surface without thermal damage to the cartilagetissue.

FIG. 10A is an illustration of an alternative embodiment of a workingend that is articulatable with an independently rotatable ablation bodyportion.

FIG. 10B is a schematic view of the working end embodiment of FIG. 10Abeing positioned in a hip joint to treat abnormal cartilage.

FIG. 11 is a schematic view of a RF generator, controller housing andperistaltic pumps corresponding to certain embodiments of the invention.

FIG. 12A is a sectional view of an alternative working end similar tothat of FIGS. 3-6, but configured with first and second polarityelectrodes disposed in the interior of the working end, wherein FIG. 12Aillustrates fluid flows within the device.

FIG. 12B is a schematic cut-away view of the working end of FIG. 12Ashowing the RF current paths which can be substantially confined to theinterior of the working end.

FIG. 13 is a schematic sectional view of another alternative working endwith a different passageway configuration that carries an interiorelectrode.

FIG. 14A is a sectional view of a ceramic core component of analternative working end with a different passageway including a valve.

FIG. 14B is a sectional view of another ceramic core component of aworking end with a different passageway including exposure to a passiveconductive or capacitive material.

FIG. 15A is a sectional view of a working end variation configured withfirst and second polarity electrodes disposed in the interior of theworking end, wherein one electrode is within an aspiration channel, withFIG. 15A illustrating fluid flows within the device.

FIG. 15B is a schematic cut-away view of the working end of FIG. 15Ashowing the RF current paths which can be substantially confined to theinterior of the working end.

FIG. 16A is a perspective view of an alternative working end configuredwith first and second polarity electrodes disposed in interior channelsand a tissue extraction lumen.

FIG. 16B is a perspective view of the working end of FIG. 16A de-matedfrom it shaft showing the flow channels in the working end.

FIG. 17A is a sectional view of the working end of FIGS. 16A-16B showinga looped inflow-outflow channels and a first polarity electrode disposedin an interior channel, and illustrating fluid flows within the workingend.

FIG. 17B is another sectional view of the working end of FIGS. 16A-16Bshowing a tissue extraction channel and a second polarity electrodedisposed in this channel, and further illustrating a fluid flow paththrough the working end.

FIG. 18A is another sectional view of the working end of FIGS. 16A-16Bshowing fluid flows within and through the working end and first andsecond polarity electrodes disposed in the interior of the working end.

FIG. 18B is a sectional view as in FIG. 18A showing the RF current pathsbetween the first and second polarity electrodes which are substantiallyconfined to the interior of the working end.

FIG. 19 is a cut-away view of an alternative working end similar to thatof FIGS. 16A-18B configured with an additional inflow channel fordelivering a saline distension fluid to a working space and analternative electrode arrangement.

FIG. 20 is a sectional view of another working end variation similar tothat of FIGS. 16A-18B with a different annular interface betweendielectric bodies configured for plasma formation therein and plasmapropagation therethrough together with an alternative electrodearrangement.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and the reference numbers marked thereon,FIGS. 1 and 2 illustrate one embodiment of chondroplasty plasma ablationdevice 100 that includes handle portion 104 and elongated shaft 105 thatextends along longitudinal axis 108. The working end 110 comprises anarticulating shaft portion 112 that allows the distal ablation bodyportion 115 to be articulated to 90° or more to thus allow the physicianto orient the distal ablation body portion 115 as needed in a joint toablate and smooth damaged regions of an articular surface, such as in aknee, hip, shoulder, ankle or other joint. In one embodiment, the shaft105 comprises an assembly of concentric thin-wall inner and outerstainless steel sleeves 120 a and 120 b with an outermost assemblydiameter of approximately 3.0 mm (FIGS. 2-3). An insulative polymerouter layer 118 is provided around the shaft 105, which can comprise aflexible temperature resistant material such as PEEK. It should beappreciated that the shaft 105 can be fabricated of a metal, polymer orcombination thereof with a diameter ranging from about 1.0 mm to 6.0 mm.Referring to FIGS. 1, 3, 4 and 5A-5B, the articulating shaft portion 112comprises inner and outer slotted sleeve portions, 122 a and 122 b, thatare coupled at distal weld 124 to thus allow axial forces to be appliedto one sleeve relative to the other sleeve to thus articulate theworking end 110 as is known in the art. In the embodiment of FIGS. 1 and2, the inner and outer slotted sleeve portions, 122 a and 122 b, canhave any configuration of slot depth, orientation and shape to provide adesired range of articulated shapes, torque resistance and the like.

In FIG. 2, it can be seen that handle grip portion 128 a can be movedtoward handle portion 128 b (from an ‘open’ position indicated at Atoward a ‘closed’ position indicated at B) to articulate the working end110. More in particular, the movement of handle portion 128 a aboutpivot 130 causes the upper handle end block 132 to engage and moveflanges 133 a, 133 b of the inner sleeve 120 b distally to thusarticulate the working end 110 between a linear shape and an articulatedshape. FIGS. 1 and 2 illustrate that the shaft 105 is rotatable relativeto handle 104 by manipulation of rotation collar 135 that is rotatablycoupled to projecting portion 136 of the handle. The moveable handleportion 128 a is further configured with a ratchet-detent member 137 athat engages detents 137 b in handle portion 128 b which is adapted toreleasably maintain the handle portions and working end 110 in aselected articulated shape. By moving the moveable handle portion 128 atoward an ‘open’ position A, the working end 110 will return to a linearconfiguration as shown in FIG. 1. Actuator buttons 138 a and 138 b areprovided in the grip portion 128 a for changing the RF power level, butalso can be configured for ON-OFF actuation of they system and RF power.

Now turning to FIGS. 3-6, the plasma generating system within theworking end 110 is shown. FIGS. 3-4 depict one example of distal plasmaablation body portion 115 in a perspective view and in a plan view. InFIGS. 3 and 4, it can be seen that the distal body portion 115 has anexpanded width relative to shaft 105 and in one embodiment can extend toa width W ranging from about 4.0 mm to 8.0 mm. FIG. 3 illustrates thatthe thickness T of the distal body portion is similar to the diameter ofshaft 105, for example about 3.0 mm.

Of particular interest, referring to FIGS. 3-6, the entirety of thedistal body portion 115 consists of electrically non-conductivematerials which can comprise ceramics or a combination of ceramic andpolymeric materials. In one embodiment shown in FIGS. 5A, 5B and 6, thebody portion 115 comprises a PEEK housing 140, annular or donut-shapedceramic element 142 that surrounds a core ceramic member indicated at144. The ceramic annular element 142 and the ceramic core 144 arepress-fit and bonded to bores in housing 140 to provide a very slightannular gap 145 having dimension G between the ceramic element 142 andceramic core 144. Of particular interest, the fluid flow restrictioncaused by the gap 145, as will be described below, is designed to focuselectrical energy density to generate plasma in gap 145. In oneembodiment, the dimension G of gap 145 is 0.02 mm, and can range fromabout 0.005 mm to 0.06 mm. In FIG. 6, it can be seen the annular gap 145transitions to slightly larger annular channel 146 having widthdimension G′ of about 0.08 mm to 0.10 mm which opens to thesubstantially planar surface 148 of body portion 115.

As will be described in detail below, the plasma ablation region 150 isadjacent and radially inward of the annular channel 146 in the planarsurface 148. The finely controlled plasma can be generated to havedifferent geometries dependent upon the operating parameters of power,fluid inflows and fluid outflows.

As described above, since the entire distal body portion 115 compriseselectrically non-conductive materials, the working end 110 in FIGS. 5A-6has its opposing polarity conductive electrodes 155A and 155B positionedremote from a plasma ablation region 150 that extends outward from gap145 and annular channel 146 of distal body portion 115. As depicted inFIGS. 3 and 5A, the plasma ablation region 150 is indicated as a‘hatched’ circular region in the center of the substantially planarsurface 148 of the distal body portion 115.

Referring now to FIGS. 5A-5B, the first polarity electrode 155Acomprises the distal portion of an interior tubular sleeve 160 of theshaft assembly. The second polarity electrode indicated at 155Bcomprises an exposed portion of outer slotted sleeve 120 a wherein aportion of the flexible outer sleeve 118 is removed. The exposed portionof sleeve 120 a that comprises the electrode can have an area rangingfrom about 1 mm² to 20 mm² and can have any shape, such as an axial,circumferential, helical or another shape.

In one embodiment depicted schematically in FIGS. 5A-5B, the firstpolarity electrode 155A is spaced proximally a distance D from thecenter or centerline 156 of the plasma ablation region 150 by at least20 mm, 30 mm, 40 mm or 50 mm. Similarly, the distal edge 158 of secondpolarity electrode 155B can be spaced proximally a distance D′ from thecenterline 156 of plasma ablation region 152 by at least 10 mm, 20 mm,30 mm, 40 mm or 50 mm (FIG. 5A).

Referring to FIGS. 5A-5B and 6, the electrical components and the meansof operation of system can be understood. In FIG. 5A, it can be seenthat a pressurized fluid source 170 is in fluid communication with lumen172 in conductive central tubular sleeve 160 which transitions into anon-conductive sleeve 175, which can be a polymeric material or aceramic. In one embodiment, the non-conductive sleeve 175 is a flexible,non-kinkable PEEK that can flex and bend as the working end isarticulated. The distal end 158 of conductive sleeve 160 is coupled tothe proximal end 176 of non-conductive sleeve 175 by any suitable meanssuch as adhesives (FIG. 6). It be seen in FIGS. 5A-5B and FIG. 6 thatlumen 172′ in sleeve 175 has an open termination 176 in chamber 177 inthe housing 140.

FIGS. 5A and 6 illustrate another electrically insulative component ofthe working end 110 that comprises flexible sleeve 180 that in oneembodiment comprises a thin-wall FEP. As can be understood, FIGS. 5A and6, the insulative FEP sleeve is adapted to provide an insulativefluid-tight layer between the first polarity electrode 150A and theslotted tubes 120 a and 120 b that are in the current carrying path tothe exposed second polarity electrode 155B. In FIG. 6, it can be seenthat the distal end 182 of the insulative sleeve 180 is bonded tosealably bonded the interior bore 184 in the housing 140.

In another aspect of the invention, still referring to FIGS. 5A-6, acirculating flow path is provided through the interior of the device(see arrows in FIG. 6) wherein positive pressure fluid source 170supplies a saline solution that flows though lumens 172 and 172′ to flowinto chamber 177 of the housing 140. Thereafter, the fluid inflowreversed course and flows in the proximal direction in annularpassageway 185 within the distal body portion 115 is coupled to negativepressure source 190 and a collection reservoir 192. A controller 195 isprovided to control the positive and negative pressures applied withinthe system to provide a selected rate of liquid flow from the fluidsource 170 through the device. The system further includes RF source 200coupled by electrical leads to the first and second polarity electrodes155A and 155B.

FIG. 7 is a schematic illustration of a method of use of the plasmaablation device of FIGS. 1-6 in treating cartilage, which is shown in aknee joint 202. Its should be appreciated that the device can be used totreat cartilage in any joint, such as knees, hips, shoulders, ankles andelbows.

FIGS. 8A-8B are cut-away schematic views of the ablation body portion115 of working end 110 and further illustrate the dimensions of‘projection’ of the plasma ablation region 150 relative to planarsurface 148 of distal body portion 115 when operated under differentparameters. In one embodiment shown in FIG. 8A, an inflow of fluidthrough lumen 172′ from source 170 is provided at a flow rate 10ml/minute. The outflow of fluid through annular lumen 185 provided bynegative pressure source 195 is provided at a flow rate greater than theinflow rate, and in this example is greater than 13 ml/minute. Thus, ifthe working end is immersed in fluid, such as in an arthroscopicprocedure, and the pressurized fluid source 170 and the negativepressure source 195 are actuated without activating the RF source 200,the device will suction fluid from the arthroscopic working space intothe interior chamber 177 of the device through annular gap 146—and thenoutwardly through lumen 185 into the collection reservoir 192. In otherwords, the inflows and outflows will not be in equilibrium when the RFis not actuated, resulting in suctioning of fluid from the workingspace. Thus, one aspect of the invention is to provide a systemcontroller 195 that operates the inflow and outflow subsystems tothereby create a substantially low pressure in chamber 177 before theactuation of RF wherein the low pressure allows for generation of aplasma ablation region 150 with unique characteristics.

FIG. 8A depicts the ablation body portion 115 operating under firstoperating parameters which results in plasma ablation region 150extending a distance P from the planar surface 148. In FIG. 8A, theoperating parameters include creating very low pressures in chamber 177,for example with outflow pressure exceeding inflow pressure by greaterthan 10%. In operation, when the plasma is generated or ignited byactuation of RF source 200, an equilibrium is created between theinflowing media through lumen 172, the outflowing media through lumen185, and the plasma projection through annular gap 146. Such anequilibrium is created after the plasma is generated, which initiallygreatly increases pressure in chamber 177. Thus, the objective of thenegative pressure source 195 is demonstrated in FIG. 8A, as the appliedsuction from negative pressure source 195 causes the plasma to form in alow (below ambient) pressure chamber with suction forces applied toionized gas (plasma) and flow media that is in a liquid or vapor state.Thus, it can be understood that such negative pressures applied tochamber 177 functions (i) to control the dimension P of the plasmaprojected from surface 148 and (ii) to cool the plasma projected fromsurface 148. FIG. 8B illustrates the plasma region 150 being projectedfrom surface 148 a certain dimension P′ which is provided by reducingthe net negative pressure applied to interior chamber 177 by inflow andoutflow subsystems. In FIG. 8B, the operating parameters includecreating a low pressure in chamber 177 wherein outflow pressure exceedsinflow pressure up to 50%.

In general, the method of the invention includes generating anequilibrium plasma in flow media within an interior of a medical deviceand controlling plasma projection outward of a working end surface aselected dimension ranging from 0.1 mm to 10 mm, or 0.5 mm to 5 mm.

In general, the invention is based on an appreciation of the fact thatan RF-generated plasma can be controllably contained in an interiorchamber 177 by providing less than ambient pressures in the interiorchamber wherein the treatment plasma can be controllable emitted from atleast one aperture that is in communication with the interior chamber.

Another aspect of the invention relating to tissue treatment is based onthe observation that a plasma can be generated by RF energy in aninterior chamber which interfaces with a negative pressure source thathas the effect of cooling the plasma. In one embodiment, the temperature(i.e., average mass temperature) of the plasma is less than 80° C., lessthan 70° C., less than 60° C., or less than 50° C.

Another aspect of the invention is based on an appreciation of the factthat the above-described device can ablate, smooth and volumetricallyremove tissue from cartilage surface without causing any thermal damageto non-targeted tissue. The energetic plasma can be generated by RFenergy in an interior chamber and then projected from the device surfaceto ablate tissue, and the lack of collateral damage results in part fromthe fact that the plasma is cooled by the low pressure chamber, with theplasma temperature being selected to be less than 80° C., less than 70°C., less than 60° C. or less than 50° C.

FIGS. 9A-9B illustrate a method of the invention in treating damagedregion 205 of articular cartilage, such as in a patient's knee as shownin FIG. 7. In FIG. 9A, a sectional view of a small a portion of apatients joint shows the cortical or subcondral bone 212, and cartilagelayer which consists of radial zone 214, transitional zone 216, andtangential zone 220. The zones 214, 216 and 220 each are characterizedby differing collagen fiber orientations with the surface zone havingcollagen fibers and fibril oriented mostly parallel to the cartilagesurface. A common form of chondromalacia or damaged cartilage is shownin FIG. 9A which consists of a fibrillated cartilage surface, whereincollagen fibril bundles 222 of the tangential zone 220 are disrupted andfibril ends 224 float outward from the cartilage surface. Such articularcartilage damage is typically only identified after an MRI scan or whenthe physician view the joint with an arthroscope. The grading ofcartilage damage uses the following nomenclature: Grade 0, the cartilageis normal and intact; Grade 1 cartilage has some softening andblistering; Grade 2 has partial thickness (less than 50%) defects orminor tears in the cartilage surface; Grade 3 has deeper defects (morethan 50%) and Grade 4 has full thickness cartilage loss with exposure ofthe subchondral bone 212.

The device of the present invention is adapted for smoothing afibrillated cartilage surface as depicted in FIGS. 9A and 9B. FIG. 9Aschematically illustrates the ablation body portion 115 introduced intosaline 126 that fills the joint space. FIG. 9A further depicts theplasma ablation region 150, which can have a temperature of less than50° C., extending outward from the device to ablate and remove thefibril ends 224 that are floating into the joint space. FIG. 9Billustrates that cartilage surface after ablation and removal of thefibril ends 224 resulting in a smooth cartilage surface. Tests have beenperformed with the device of FIGS. 5A-9B on human cartilage tissueimmediately after such tissue was removed from a patient in a ‘totalknee’ replacement operation. It was found that the treated cartilagesurface was very smooth when compared to prior art bi-polar electrodedevices with exposed electrodes. In another important aspect of theinvention, tests have shown that the plasma region 150 as depicted inFIGS. 9A-9B produce no thermal effects or cell death in the cartilagesurface. Tests were performed using confocal laser microscopy asdescribed in Edwards, R, “Thermal Chondroplasty of Chondromalacic HumanCartilage An Ex Vivo Comparison of Bipolar and Monopolar RadiofrequencyDevices,” The American Journal of Sports Medicine (2002) Vol. 30, No. 1,p 90. In tests of the present invention, no significant chondrocytedeath was found as determined by cell viability staining in conjunctionwith confocal laser microscopy methods. In contrast, in the Edwardsarticle above, all prior art RF devices that were tested causedsubstantial cell death in cartilage tissue.

FIG. 10A illustrates another embodiment of working end 110′ wherein theablation body portion 115 is rotatable relative to shaft 105 no matterhow the shaft is articulated. This is accomplished by providing anadditional rotatable, torque-able sleeve 230 that carries the ablationbody portion 115 and is rotatable within outer articulating sleeveassembly 232. FIG. 11 is a schematic illustration of the working end ofFIG. 10A being used in a hip joint 240, wherein the device is introducedthrough an access cannula 245. After being deployed in the joint spacewith the introducer shaft 105 being articulated, the ablation end 115can be rotated (see arrow) to orient the plasma to treat targetedcartilage tissue.

FIG. 11 illustrates a controller box or housing 300 that combines an RFgenerator source 310, computer controller 315 and positive and negativepressure subsystems configured for operating the ablation devicesdescribed above and below. The RF source 310 can be a conventionalgenerator as is known in the art operates at within the range of 100 kHzto 550 kHz, and in one embodiment operates at 150 kHz. The front panelof controller housing 300 carries the exposed roller pump portions offirst and second peristaltic pumps 316 and 318 as are known in the artthat can be configured as the positive and negative pressure subsystems.The controller and ablation system can be operated from the touch screendisplay 320. FIG. 11 further shows single-channel or multi-channel tubes322 and 324 that are detachably coupled to each peristaltic pump 316 and318 to deliver positive pressure and negative pressure to the ablationdevice (see FIG. 1). The system further includes a fluid or salinesource 330 connected to a positive pressure source to provide fluidinflows to the ablation device and a collection reservoir 335 associatedwith at least one negative pressure source to collect aspirated fluidand ablation by products. A footswitch 340 is provided for ON-OFFoperation of the system and the RF source, although operating controlsalso can be provided in the handle of the device.

FIGS. 12A-12B illustrate another variation of a plasma ablation workingend 400 that configured for chondroplasty procedures. The working end400 of FIG. 12A is carried at the distal end of shaft 405 and is basedon the same operational principles described above in the embodiment ofFIGS. 3-6. The shaft 405 extends about axis 406 and can comprise athin-wall stainless steel tube 407 with insulative inner and outercoatings or layers 408 and 408′. The variation of FIGS. 12A-12B differsin that both first and second polarity electrodes, 410A and 410B, aredisposed in interior passageways or regions of the device remote fromarticular tissue targeted for treatment. This configuration of theopposing polarity electrodes 410A and 410B provides for increasedcontrol over RF current paths in the immersed working space whichconsists of saline 412. More particularly, the electrode configurationcan confine RF current paths substantially to the interior channels ofthe working end 400 and thus limit RF energy density in articular tissueto prevent active Joule heating of such tissue. In other words, theworking end variation of FIGS. 12A-12B insures that targeted tissue canbe treated with a low temperature plasma alone, which can best bedescribed as “plasma etching” of such articular tissue. Such plasmaetching can smooth the cartilage surface without causing thermal damageto cartilage below the articular surface.

The embodiment of FIGS. 12A-12B has a distal body portion or housing 415that consists of electrically non-conductive materials such as a ceramicor polymer. In the embodiment shown in FIG. 12A, the housing portion 415is a ceramic mated with an annular, donut-shaped ceramic element 418that partly surrounds a core ceramic member 420. The annular element 418and ceramic core 420 extend transversely through interior chamber 422and are bonded in bores 424 a and 424 b in housing 415 to provide thesmall annular gap 425 as described previously in which plasma formationis initiated. The annular gap 425 has a dimension as described above tofunction as a flow restriction wherein plasma 430 (FIG. 12B) can becontrollably ignited as described in the previous embodiment. In FIG.12A, it can be seen that the annular gap 425 transitions into annularchannel 432 which has an open termination indicated at 435 from whichplasma is projected outwardly. In this embodiment, the open termination435 is within a recess or concavity 436 in the surface or perimeter 438of body portion 415. More in particular, the open termination 435 isspaced inwardly from surface 438 a recessed dimension RD that can rangefrom 0.5 mm to 5.0 mm. In operation, the system parameters can bemodulated to cause the plasma to be projected outwardly a selecteddimension from the open termination 435 of annular channel 432 into theconcavity 436.

Still referring to FIG. 12A, the circulating saline flow paths areprovided through the interior of the device (see dotted lines and arrowsin FIG. 12A) wherein positive pressure fluid source 440 supplies asaline solution that flows though lumen or first channel 442 ininsulative sleeve 444 into chamber 422 of the housing 415. Thereafter,the fluid inflow reverses course in the interior chamber 422 which mayalso be described as a flow transition zone herein. The fluid then canflow in the proximal direction in the concentric passageway or secondchannel 445 that extends through the distal body portion 415 and shaft405 and is coupled to negative pressure source 450 and collectionreservoir 335 (see FIG. 11). As can be seen in FIGS. 12A, the interiorchamber 432 or transition zone also communicates with annular gap 425and annular channel 432 which also is called a third channel herein. Acontroller 455 is provided to control the positive and negativepressures applied within the system to provide a selected rate of liquidflow from the fluid source 440 through the device. The system furtherincludes RF source 460 that is operatively connected to the first andsecond polarity electrodes, 410A and 410B. As can be seen in FIGS. 12Aand 12B, the second polarity electrode 410B is positioned in theinterior of a passageway 462 that extends transverse to the axis of theshaft 405 with open ends on both sides of the working end. Thus, thepassageway 462 has a dimension and configuration that permits saline 412to flow into the passageway 462 as soon as the working end is immersedand thus electrode 410B will be in contact with the conductive saline412 in the working space while the electrodes is maintained spaced apartfrom targeted tissue.

In another aspect of the invention, referring to FIG. 12B, it can beseen that RF current paths CP can extend from first polarity electrode410A through interior chamber 422 and annular channel 432 to the secondpolarity electrode 410B in passageway 462 without extendingsubstantially outward from the exterior surface 438 of the working end.This aspect of the invention allows for control of plasma as it projectsoutward from exits annular channel 432 and can confine plasma with therecess 436 in the surface which in turn can control any potential RFenergy density is tissue. The plasma's geometry further can becontrolled by modulating the operating parameters of applied RF power,fluid inflows and fluid outflows which control operating pressure ininterior chamber 422.

Referring to FIGS. 12A-12B, the looped inflow and outflow subsystemsprovide operating parameters as described previously wherein very lowpressures can be created in interior chamber 422 during plasmageneration, for example with outflow pressures exceeding inflowpressures by greater than 10%. In one aspect of the invention, thenegative pressure source 450 functions to modify the plasma (initiatedin gap 425 and then extended outwardly through channel 432) from avolatile plasma to a non-volatile plasma. The term ‘volatile’ plasma, asused herein, is meant to describe the gaseous plasma media in itsdynamic phase-transitioning stage, as saline is phase-transitionedinstantly form liquid to water vapor and then to an ionized gas. In sucha phase-transitioning or ‘volatile’ plasma, there is substantialpopping, bubble formation and bubble collapse. Such a volatile plasmawith bubble formation and collapse is undesirable in the volume ofsaline 412 that fills and comprises the working space (FIGS. 12A-12B).Thus, it can be understood the negative pressures applied to chamber 422can function to suction the bubbles and liquid media from the volatileplasma in the interior chamber 422 to thereby create a non-volatile,non-bubbling plasma that can be extended through annular channel 232 tointerface with targeted tissue. As described above, the negativepressures applied to interior chamber 422 additionally function (i) tocontrol the dimension or geometry of the plasma projected outward fromopen termination 435 of the annular channel 432 and (ii) to cool theplasma projected from channel 432. In FIGS. 12-12B, the operatingparameters include creating a low pressure in chamber 422 whereinoutflow pressure from negative pressure source 450 exceeds inflowpressure of saline by at least 10%, 20%, 30%, 40% and 50%.

In general, a method corresponding to invention comprises creating anon-volatile plasma in an immersed conductive fluid workspace andinterfacing the non-volatile plasma with targeted tissue. The methodcomprises ablating a targeted body structure with a non-volatile,non-bubbling plasma in a fluid environment which permits endoscopicviewing in the non-bubbling environment. More in particular, the methodincludes positioning a probe working end in proximity to a targetedstructure of a patient's body, wherein the working end includes aninterior space, and creating a volatile plasma in the interior space andextending a non-volatile plasma outwardly from the interior space tointerface with the targeted structure. The method includes modifying aplasma from volatile to non-volatile. The method further includesmodifying the plasma by applying negative pressure to the volatileplasma to remove bubbles and liquid from the volatile plasma. The methodincludes igniting the plasma in flow media flowing in a looped flowthrough the interior space 422 in a device working end (FIGS. 12A-12B).

FIG. 13 is a cut-away view of another embodiment of working end 400′that is similar to the embodiment depicted in FIGS. 12A-12B, in whichlike reference numbers indicate like features. The variation in FIG. 13differs only in the configuration of the transverse passageway inceramic core 420 that extends transverse to the axis 406 of shaft 405and that carries electrode 410B. In FIG. 13, it can be seen that thetransverse passageway has a non-uniform cross-section with largerdiameter portion 472 transitioning to smaller diameter portion 474. Thisvariation is adapted to substantially prevent saline flows through thetransverse passageway during a treatment interval which might be inducedby saline or plasma flows in annular channel 432. The variation of FIG.13 also shows the open termination 435 of the annular channel 432 iswithin a smooth contour concavity 475 in the working end.

FIGS. 14A-14B illustrate alternative ceramic cores 420′ and 420″ thatcan be used in the working end embodiments of FIG. 12A or FIG. 13. Thevariations of FIGS. 14A-14B are again adapted to control saline flow inthe transverse passageway in the ceramic core while still insuring thata conductive path is provided interior electrode 410B which is exposedto the passageway. In FIG. 14A, it can be seen that the transversepassageway 482 has a flap-valve 485 or any type of one-way valve intransverse passageway portion 486 to limit, but permit, saline flowsinto and/or through the passageway. FIG. 14B depicts a closed-endpassageway 492 that carries electrode 410B. In FIG. 14B, the closed end494 of the passageway interfaces with a conductive or capacitivematerial 496 that is not coupled to electrode 410B but can potentiallycarry current to saline in the passageway 492. It should be appreciatedthat the open end of the passageways 482 and 492 in FIGS. 14-14B can beoriented in either direction relative to opening 435 of annular channel432.

FIGS. 15A-15B are cut-away views of another embodiment of working end500 that is similar to the embodiment depicted in FIGS. 12A-12B andagain in which like reference numbers indicate like features. Theembodiment of variation in FIGS. 15A-15B includes opposing polarityelectrodes 510A and 510B disposed within active fluid flow passagewaysin the interior of the working end 500. In this embodiment, a secondnegative pressure source 515 is provided which is configured to suctionflow media and fibrillated cartilage into an interface with plasmaprojecting outward from the opening 435 of annular channel 432. Further,the second negative pressure source 515 can extract ablation debris andbubbles from saline 412 during operation. More in particular, the secondnegative pressure source 515 is coupled to aspiration lumen or fourthchannel 520 in insulative sleeve 522 that extends to opening 524 intransverse passageway 532 within the ceramic cores 420. As can be seenin FIG. 15A, the saline inflow from source 440 is similar to previousembodiments wherein circulating saline inflows and outflows are providedthrough inflow channel 536 in insulative sleeve 538 and thereafterthrough interior chamber 422 and outflow channel 540. In thisembodiment, the first polarity electrode 510A is carried in inflowchannel 536 and the second polarity electrode 510B is carried inaspiration channel 520. FIG. 15A shows the various flow channels asbeing concentric for convenience, and it should be appreciated that anyconfiguration of the multiple channels can be used.

In operation, FIG. 15A indicates the various fluid flows by dotted linesand arrows. In FIG. 15B, the RF current paths CP are shown duringoperation in the same manner as shown in FIG. 12B to illustrate theformation of plasma 445 in the flow restriction. As can be seen in FIG.15B, the RF current path extends from first electrode 510A exposed tosaline in flow channel 536 through the flow restriction 425 (see FIG.15A) and then through transverse passageway 532 and lumen 520 to secondelectrode 510B. As in the embodiment of FIGS. 12A-12B, the RF currentpaths are substantially confined to the interior of the working endwhich lowers or eliminates RF current density in tissue. In all otherrespects, the working end 500 functions as described previously.

FIGS. 16A-18B illustrate another electrosurgical system 600 and workingend 605 that is adapted for chondroplasty procedures. In FIG. 16, it canbe seen that a round or oval probe shaft 610 carries a dielectricworking end 605 that can comprises ceramic bodies as generally describedabove. The shaft 610 can comprise a stainless steel tube covered with athin wall dielectric material 611. In one embodiment, the distal workingend 605 comprises an assembly of first and second ceramic bodies 612Aand 612B (e.g., zirconium) that define an interface 615 therebetween.Both ceramic bodies 612A and 612B are carried in ceramic housing 614.The interface 615 between the ceramic bodies 612A and 612B (see FIG.18A), terminating in gap G in the surface 618, can be extremely tightand in one embodiment the interface is sufficiently fluid-tight toprevent liquid flow therethrough but still permit electrons and plasmato propagate through the interface 615. In working end 605 of FIGS.16A-18B, the first and second polarity electrodes, 620A and 620B aredisposed entirely within the interior of ceramic bodies 612A and 612Bwith no exposure in the working surface 618 or shaft 610.

Now turning to FIG. 16B, the ceramic working end 605 is shown de-matedfrom the shaft 610. In FIG. 16B, it can be seen that there is a loopedor circulating first inflow channel 622A and second outflow channel 622Bwherein a positive pressure source 625 delivers saline solution throughfirst channel 622A and around the interior channel portion 630 (see FIG.17A) adjacent the interface 615 between ceramic bodies 612A and 612B(see FIG. 18A). A negative pressure source 635 is configured to draw orsuction the saline through channel 622B to a remote collectionreservoir. In addition, the negative pressure source 635 communicateswith a tissue extraction lumen 640 in the probe shaft and working end605 which has an open termination 644 in working surface 622. In oneembodiment, a single negative pressure source 635 is used to communicatewith both (i) the saline outflow through second channel 622B and (ii)saline outflow through the tissue extraction channel 640. As will bedescribed below, one embodiment provides pressure and/or a flow controlmechanism positioned intermediate the negative pressure source 635 andthe tissue extraction channel 640. In one such embodiment, the pressurecontrol mechanism comprises a check valve 648 shown schematically inFIG. 16B. Such a check valve or pressure relief valve 648 can bedisposed in the working end 605 or in the shaft 610 or in a handle ofthe device (not shown). The check valve can function to maintainnegative pressure parameters in the second channel 622B and channelportion 630 (see FIGS. 17A and 18A) to maintain predetermined plasmaignition parameters in the event the tissue debris clogs the tissueextraction lumen 640.

Now turning to FIG. 17A, a sectional view is provided through a portionof the working end 605 of FIG. 16B and more particularly through theinflow and outflow channels 622A and 622B. It can be seen how thepositive pressure source 625 introduces saline through first channel622A and then around the looped channel portion 630 adjacent theinterface 615 between the ceramic bodies 612A and 612B to finally flowinto the outflow channel 622 b assisted by the negative pressure source635. The plasma can be controlled to project through the interface 615to the working surface 618. FIG. 17A a further shows a first polarityelectrode 650A disposed in the inflow channel 622A from which RF currentcan flow through the interface 615 as will be described below. Theelectrode 650A is operatively coupled to RF source 655 and controller660.

FIG. 17B is another section through working end 605 and moreparticularly through the tissue extraction channel 640 in the workingend of FIG. 16B. It can be seen that the single negative pressure source635 is in fluid communication with the proximal end of the tissueextraction lumen 640 as well as the second channel 622B described above.Further, a second polarity electrode 650B is disposed within the tissueextraction channel 640 so that both polarity electrodes are entirelyinternal to the working end 605.

FIGS. 18A-18 b are cut-away views of working end 605 that show fluidflows and RF current paths within the working end in using the probe totreat damaged cartilage or similar tissue. Referring to FIG. 18A, theworking end 605 is shown disposed in a distending fluid, such as asaline solution, in a working space 662. The dotted lines in FIG. 18Aindicate potential and actual fluid flows within the working end andthrough the working end 604 from the working space. FIG. 18A shows thatthe negative pressure source 635 is coupled to both the tissueextraction lumen 640 and the outflow lumen 622B. The purpose of thepressure control mechanism or pressure relief valve 648 can be betterunderstood from FIG. 18A. The probe and working end 605 are designed tosmooth cartilage in a working space 662 and in some instances the plasmamay ablate and extract fibrillations that will clog the tissueextraction lumen 640. In such an instance, there will be an imbalance inthe negative pressure source 635 applying suction pressures to bothchannels 622B and 640. Thus, one embodiment uses as pressure reliefvalve 648 which can prevent excessive negative pressure from beingdirected to the second channel 622B when the extraction channel 640 isclogged in which case the excessive negative pressure would alter ordiminish plasma formation. In another embodiment, at least one optionalpressure sensor 670 (FIG. 18B) can be provided to sense pressure ineither or both channels 622B and 640 wherein the sensor can beconfigured to signal the controller to modulate a valve (not shown) tomaintain a predetermined pressure in the second channel 622B to therebymaintain plasma formation in the interface 615. In another embodiment,referring to FIG. 19, the probe can have first and second independentlycontrolled negative pressure sources 635 and 635′ coupled to respectiveoutflow channel 622B and tissue extraction channel 640. In anotherembodiment, the tissue extraction channel can carry a pressure sensor670 as described previously (see FIG. 18B) wherein the sensor can sensetissue clogging the channel in which case the controller 660 wouldmodulate pressure in the channel between greater negatives pressures,pulsed negative pressures, positive inflow pressures, pulsed inflowpressures, or a combination of such pressure modulations designed toremove the tissue debris clogging the channel 640.

FIG. 18B illustrates the current paths CP within and about the workingend 605 during operation in which plasma is generated and translatedacross a tissue surface. As can be seen in FIG. 18B, both the sleevelike electrodes 650A and 650B are disposed in channels 622A and 640,respectively, in the working end 605 and the RF current paths CPcommunicates though channel 622A, interface 615 and extraction channel640 to provide for plasma-tissue contact while both electrodes 650A and650B are disposed in the interior of the working end 605. Thus, theworking end 605 and system creates RF current paths CP that are confinedwithin the working end and extend only slightly into or around a portionof the working surface 618 of the probe. In one aspect of the invention,the fact that both electrodes 650A and 650B are completely internalwithin the working end means the no high energy densities are createdabout an electrode adjacent to or in contact with tissue. This in turnmeans that tissue cannot be heated to high temperatures or carbonizedwhich is undesirable and can lead to elevated immune responses and delayhealing of treated tissue.

FIG. 19 illustrates another system and working end embodiment 680 whichis similar to that of FIGS. 16A-16B except that this embodiment includesa further inflow channel 682 for delivering a saline distention fluidthrough probe and outwardly from the working end. In this embodiment,another internal saline flow is provided in the paths as previouslydescribed circulating through inflow channel 622A, loop channel portion630 and outflow channel 622B. The tissue extraction channel 640 is againas described previously. The variation in FIG. 19 has first and secondnegative pressure sources 635 and 635′ independently coupled to channel622B and 640. The distension fluid channels 682 in FIG. 19 isoperatively coupled to a second positive pressure source 625′ whichprovides the saline distention fluid. In the working end 680 of FIG. 19,the opposing polarity electrodes 650A and 685 are disposed entirelywithin the interior of the device. In one embodiment, the first polarityelectrode 650A again is carried in inflow channel 622A and the secondpolarity electrode 685 is carried in the distension fluid inflow channel682. In operation, it can be understood that current paths CP (notshown) will extend from first polarity internal electrode 650A throughinterface 615 and inflow channel 682 to the second polarity internalelectrode 685.

FIG. 20 illustrates another working end 700 embodiment that is similarto that of FIGS. 16A-18B except that the opposing polarity first andsecond electrodes 705A and 705B have a different configuration—stillpositioned within the interior channels of the working end 700. As canbe seen in FIG. 20, the inflow and outflow channels 622A and 622B aresimilar to previous embodiments. The working end 700 further has a fluidextraction channel 640 as described previously. In one variation, theworking end 700 has a looped wire first polarity electrode 705Aextending through the working end through first inflow channel 622B,around looped channel portion 630 adjacent interface 615 and extendingpartly through second outflow channel 622B. In the working end 700 ofFIG. 20, both the first and second electrodes 705A and 705B are roundwires with large surface areas which enhances RF current flow in thefluid environment. This electrode configuration provides an increasedsurface area to the electrode and extends such an electrode surfacearound the region of plasma ignition which together with the absence ofsharp edges can enhance the uniformity of the plasma generation in theinterface 615. The electrode 705A can have any suitable diameter rangingfrom about 0.005″ to 0.10″. Similarly, the second polarity electrode705B is configured to have a substantial exposed surface with a length,for example, ranging from 2 mm to 20 mm (and diameter of about 0.005″ to0.10″) in the tissue-extraction channel 640. The distal end 708 of theelectrode 705A is embedded and sealed into ceramic housing 614 toprevent any sharp electrode edges exposed to the channel 640.

As can be understood from FIG. 20, the RF current paths CP between thefirst and second polarity electrodes 705A and 705B extends through theinterface 615 between the ceramic bodies 612A and 612Bt as describedpreviously. In another aspect of the invention, still referring to FIG.20, the interface 615 has a greatly increased surface area compared toprevious embodiments. It can be seen in FIG. 20 that a tapered annualinterface 615 is provided between the dielectric bodies 612A and 612Bwhich after assembly comprises an extremely small gap. In oneembodiment, the interface is dimensioned to be sufficiently fluid-tightto prevent liquid flow therethrough and will only permit current flowsand plasma propagation therethrough. In this embodiment, the taperedinterface or taper lock between the first and second dielectric bodies612A and 612B is provided by a predetermined surface roughness that isfabricated on either or both dielectric bodies 612A and 612B at eitherside of the interface 615. In other words, the first and seconddielectric bodies 612A and 612B are wedged together tightly with amicron or sub-micron dimensioned gap between the surface finishes of themating dielectric bodies.

In one embodiment, the interface 615 is annular as shown in FIG. 20 andextends between a first interior periphery 710 of the interface 615 anda second exterior periphery 715 of the interface wherein the meandimension between the inner and outer peripheries ranges from 0.005″ to0.25″. Although the variation of FIG. 20 illustrates an annularinterface 615, the scope of the invention includes any interfaceconfiguration such as a linear configuration, an oval configuration, anyelongated configuration, or a polygonal or star-shaped configuration.The total area of such an interface 615 can be from 0.01 mm² to 10 mm².

In general, a method of ablating tissue corresponding to the inventioncomprises providing an electrosurgical working end with an interiorchamber communicating with a working surface through a space that issufficiently fluid-tight to prevent liquid flow therethrough but permitplasma propagation therethrough, igniting a plasma in the gap utilizingfirst and second opposing polarity electrodes positioned on either sideof the gap, and controlling propagation of the plasma through the gap tointerface with tissue. In one aspect of the invention, the plasmapropagation is controlled by controlling pressure interior of the gap.In another aspect of the invention, the plasma propagation is controlledby controlling the dimensions of said gap which can comprised the widthor cross section of the gap and/or the dimension between the inner andouter peripheries of the gap.

Although particular embodiments of the present invention have beendescribed above in detail, it will be understood that this descriptionis merely for purposes of illustration and the above description of theinvention is not exhaustive. Specific features of the invention areshown in some drawings and not in others, and this is for convenienceonly and any feature may be combined with another in accordance with theinvention. A number of variations and alternatives will be apparent toone having ordinary skills in the art. Such alternatives and variationsare intended to be included within the scope of the claims. Particularfeatures that are presented in dependent claims can be combined and fallwithin the scope of the invention. The invention also encompassesembodiments as if dependent claims were alternatively written in amultiple dependent claim format with reference to other independentclaims.

What is claimed is:
 1. A system for treating a target tissue, saidsystem comprising: a probe having an interior space and a working endwith a working surface; means for igniting a plasma within the interiorspace, wherein the plasma propagates outwardly from the working surface;and means for exposing the target tissue to the plasma.
 2. A system asin claim 1, wherein the interior space comprises a gap in the workingend of the probe.
 3. A system as in claim 2, wherein the means forigniting the plasma comprises means for igniting a conductive mediapassing through the gap.
 4. A system as in claim 3, wherein the gap hasan interior periphery and an exterior periphery with a spacingtherebetween which is sufficiently fluid tight to inhibit liquid flowbut permit plasma propagation therethrough.
 5. A system as in claim 4,wherein the means for igniting the plasma applies electrical energy tothe conductive media from opposite polarity electrodes.
 6. A system asin claim 5, wherein the means for igniting the plasma comprises a firstpolarity electrode is disposed in proximity to the inner periphery.
 7. Asystem as in claim 6, wherein the first polarity electrode is disposedin a fluid channel in communication with said inner periphery.
 8. Asystem as in claim 7, wherein the means for igniting the plasma furthercomprises a second polarity electrode in the working end in potentialfluid communication with said exterior periphery.
 9. A system as inclaim 4, wherein a mean dimension between said interior and exteriorperipheries of the interface is from 0.005 inch to 0.25 inch.
 10. Asystem as in claim 4, wherein the total area of the interface is from0.01 mm to 10 mm².
 11. A system as in claim 4, wherein the gap has anannular configuration, a linear configuration, an oval configuration, anelongated configuration, or a star-shaped configuration.
 12. A system asin claim 3, further comprising means for controlling a rate ofpropagation through the gap.
 13. A system as in claim 12, wherein themeans for controlling a rate of propagation through the gap controls adimension of said gap.
 14. A system as in claim 13, wherein the meansfor controlling a rate of propagation through the gap controls a widthof said gap.
 15. A system as in claim 14, wherein the means forcontrolling a rate of propagation through the gap controls a dimensionof said gap between a plasma ignition region and the working surface.16. A system as in claim 12, wherein the means for controlling a rate ofpropagation through the gap varies a pressure of the conductive media inthe interior space.
 17. A system as in claim 16, wherein the conductivemedia is introduced into the interior space under a controlled pressure.18. A system as in claim 16, wherein the conductive media is removedfrom the interior space under a controlled negative pressure.
 19. Asystem as in claim 1, wherein the means for igniting a plasma within theinterior space establishes a continuous loop flow of a conductive mediathrough the interior space wherein a portion of the conductive media isignited within the interior space and a remainder exists the interiorspace.
 20. A system as in claim 19, wherein the conductive media entersthe interior space through an inlet flow channel in the probe, theremainder exits through an outlet flow channel in the probe, and theplasma exits through one or more gaps in the working end.
 21. A systemas in claim 20, wherein a propagation rate of the plasma is controlledby varying the inlet pressure of conductive media in the inlet channeland an outlet pressure of conductive media in the outlet channel.
 22. Asystem as in claim 20, wherein the plasma is ignited by passing currentsthrough opposed polarity electrodes in the interior space.
 23. A systemas in claim 22, wherein the interior space comprises a channeltransition zone between the inlet and outlet channels.
 24. A system asin claim 23, wherein the channel transition zone comprises a flowrestriction.
 25. A system as in claim 24, wherein the plasma is ignitedat said flow restriction.